One possible cause of failure of fluorescent lamps is a reduced emission capacity of the electrodes (what is known as the “end of life effect”). This effect occurs at the end of the service life of a fluorescent lamp at one of the two electrodes. This leads to the discharge current flowing more lightly through the lamp in one direction than in the opposing direction. In this case the fluorescent lamp functions as a rectifier. The electrode which is not capable of emission is heated so much in the process that high temperatures can occur at the lamp surface. In an extreme case the glass tube can melt in the case of fluorescent lamps with a small diameter.
An electronic ballast (EB) for actuation of the fluorescent lamp must detect such a fault in good time and either limit output current and output voltage respectively to an uncritical value or turn off the fluorescent lamp.
Above and beyond actual lamp operation the EB must fulfill various control and monitoring functions. Separate circuit components are required for such control and monitoring functions—in particular according to the circuit of the EB.